Printing apparatus, method and storage medium for conveying sheets intermittently to printhead while conveyed sheets partially overlap

ABSTRACT

A printing apparatus includes a first feeding roller, a feeding motor configured to drive the first feeding roller, a second feeding roller, a conveyance roller, a conveyance motor configured to drive the conveyance roller, a printing unit configured to print the printing sheet, a detection sensor configured to detect the leading edge of the printing sheet, and a control unit configured to, when the printing unit performs a printing operation on a preceding sheet, drive the feeding motor in synchronization with the conveyance motor before the detection sensor detects the leading edge of a succeeding sheet, and continuously drive the feeding motor so that the conveying speed of the succeeding sheet by the feeding motor becomes higher than that of the preceding sheet after the detection sensor detects the leading edge of the succeeding sheet.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates to a printing apparatus for printing asheet by a printhead and, more particularly, to a printing apparatus forconveying sheets to a printing area facing a printhead while part of asucceeding sheet overlaps part of a preceding sheet.

Description of the Related Art

Japanese Patent Laid-Open No. 2000-15881 describes a printing apparatusfor controlling to make the marginal area of the leading edge of asucceeding sheet overlap the marginal area of the trailing edge of apreceding sheet, which comprises a feeding means for separating andfeeding a plurality of sheets one by one, a printing means for formingan image on a sheet, a conveyance means for conveying a sheet to theprinting means, a detection means for detecting a sheet, and a controlmeans for controlling driving of the feeding means according to a signalof the detection means.

However, the apparatus described in Japanese Patent Laid-Open No.2000-15881 can start to feed a succeeding sheet only when the marginalamount of the trailing edge of the preceding sheet and the marginalamount of the leading edge of the succeeding sheet are confirmed beforethe start of feeding of the succeeding sheet. This imposes a technicalproblem that it takes time to start to feed the succeeding sheet.

SUMMARY OF THE INVENTION

The present invention has been made in consideration of theabove-described problem, and provides a printing apparatus which canperform a chasing operation to make a succeeding sheet overlap apreceding sheet.

According to the first aspect of the present invention, there isprovided a printing apparatus comprising: a first feeding rollerconfigured to feed a printing sheet stacked on a stacking unit; afeeding motor configured to drive the first feeding roller; a secondfeeding roller driven by the feeding motor and configured to convey theprinting sheet fed by the first feeding roller; a conveyance rollerconfigured to convey the printing sheet conveyed by the second feedingroller; a conveyance motor configured to drive the conveyance roller; aprinting unit configured to print the printing sheet conveyed by theconveyance roller; a detection unit, arranged between the second feedingroller and the conveyance roller, configured to detect a leading edge ofthe printing sheet; and a control unit configured to, when the printingunit performs a printing operation on a preceding sheet as a printingsheet precedingly fed from the stacking unit, drive the feeding motor insynchronization with the conveyance motor before the detection unitdetects a leading edge of a succeeding sheet as a printing sheetsucceedingly fed from the stacking unit, and continuously drive thefeeding motor so that a conveying speed of the succeeding sheet by thefeeding motor becomes higher than a conveying speed of the precedingsheet by the conveyance motor after the detection unit detects theleading edge of the succeeding sheet.

According to the second aspect of the present invention, there isprovided a printing apparatus comprising: a first feeding rollerconfigured to feed a printing sheet stacked on a stacking unit; afeeding motor configured to drive the first feeding roller; a secondfeeding roller driven by the feeding motor and configured to convey theprinting sheet fed by the first feeding roller; a conveyance rollerconfigured to convey the printing sheet conveyed by the second feedingroller; a conveyance motor configured to drive the conveyance roller; aprinting unit configured to print the printing sheet conveyed by theconveyance roller; a carriage incorporating the printing unit to move ina direction intersecting a direction in which the printing sheet isconveyed; a printing control unit configured to print an image on theprinting sheet by repeating an operation of intermittently conveying theprinting sheet by the conveyance roller and an operation of moving thecarriage in the intersecting direction; a detection unit, arrangedbetween the second feeding roller and the conveyance roller, configuredto detect a leading edge of the printing sheet; and a control unitconfigured to, when the printing unit performs a printing operation on apreceding sheet as a printing sheet precedingly fed from the stackingunit, intermittently drive the feeding motor in synchronization with theconveyance motor before the detection unit detects a leading edge of asucceeding sheet as a printing sheet succeedingly fed from the stackingunit, and continuously drive the feeding motor after the detection unitdetects the leading edge of the succeeding sheet.

According to the third aspect of the present invention, there isprovided a method of controlling a printing apparatus including a firstfeeding roller configured to feed a printing sheet stacked on a stackingunit, a feeding motor configured to drive the first feeding roller, asecond feeding roller driven by the feeding motor and configured toconvey the printing sheet fed by the first feeding roller, a conveyanceroller configured to convey the printing sheet conveyed by the secondfeeding roller, a conveyance motor configured to drive the conveyanceroller, a printing unit configured to print the printing sheet conveyedby the conveyance roller, and a detection unit, arranged between thesecond feeding roller and the conveyance roller, configured to detect aleading edge of the printing sheet, the method comprising: a controlstep of, when the printing unit performs a printing operation on apreceding sheet as a printing sheet precedingly fed from the stackingunit, driving the feeding motor in synchronization with the conveyancemotor before the detection unit detects a leading edge of a succeedingsheet as a printing sheet succeedingly fed from the stacking unit, andcontinuously driving the feeding motor so that a conveying speed of thesucceeding sheet by the feeding motor becomes higher than a conveyingspeed of the preceding sheet by the conveyance motor after the detectionunit detects the leading edge of the succeeding sheet.

According to the fourth aspect of the present invention, there isprovided a method of controlling a printing apparatus including a firstfeeding roller configured to feed a printing sheet stacked on a stackingunit, a feeding motor configured to drive the first feeding roller, asecond feeding roller driven by the feeding motor and configured toconvey the printing sheet fed by the first feeding roller, a conveyanceroller configured to convey the printing sheet conveyed by the secondfeeding roller, a conveyance motor configured to drive the conveyanceroller, a printing unit configured to print the printing sheet conveyedby the conveyance roller, a carriage incorporating the printing unit tomove in a direction intersecting a direction in which the printing sheetis conveyed, printing a control unit configured to print an image on theprinting sheet by repeating an operation of intermittently conveying theprinting sheet by the conveyance roller and an operation of moving thecarriage in the intersecting direction, and a detection unit, arrangedbetween the second feeding roller and the conveyance roller, configuredto detect a leading edge of the printing sheet, the method comprising: acontrol step of, when the printing unit performs a printing operation ona preceding sheet as a printing sheet precedingly fed from the stackingunit, intermittently driving the feeding motor in synchronization withthe conveyance motor before the detection unit detects a leading edge ofa succeeding sheet as a printing sheet succeedingly fed from thestacking unit, and continuously driving the feeding motor after thedetection unit detects the leading edge of the succeeding sheet.

Further features of the present invention will become apparent from thefollowing description of exemplary embodiments with reference to theattached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a view for explaining an overlap continuous feeding operationin a printing apparatus according to the first embodiment of the presentinvention;

FIG. 2 is a view for explaining the overlap continuous feeding operationin the printing apparatus according to the first embodiment of thepresent invention;

FIG. 3 is a view for explaining the overlap continuous feeding operationin the printing apparatus according to the first embodiment of thepresent invention;

FIGS. 4A and 4B are views for explaining the arrangement of a pickuproller;

FIG. 5 is a block diagram showing the printing apparatus according tothe first embodiment;

FIGS. 6A and 6B are flowcharts illustrating the overlap continuousfeeding operation according to the first embodiment;

FIG. 7 is a view for explaining an operation of making a succeedingsheet overlap a preceding sheet;

FIG. 8 is a view for explaining the operation of making the succeedingsheet overlap the preceding sheet;

FIG. 9 is a flowchart for explaining the skew correction operation ofthe succeeding sheet according to the first embodiment;

FIG. 10 is a flowchart for explaining an operation of calculating theleading edge position of the succeeding sheet; and

FIGS. 11A to 11C are views for explaining an overlap continuous feedingoperation according to the second embodiment.

DESCRIPTION OF THE EMBODIMENTS

Embodiments of the present invention will be described in detail belowwith reference to the accompanying drawings.

First Embodiment

FIGS. 1 to 3 are sectional views for explaining an overlap continuousfeeding operation in a printing apparatus according to the firstembodiment of the present invention. The schematic arrangement of theprinting apparatus according to the embodiment will first be describedwith reference to ST1 of FIG. 1.

In ST1 of FIG. 1, reference numeral 1 denotes printing sheets. Theplurality of printing sheets 1 are stacked on a feeding tray 11 (astacking unit). A pickup roller 2 abuts against the top printing sheet 1stacked on the feeding tray 11 to pick it up. A feeding roller 3 feedsthe printing sheet 1 picked up by the pickup roller 2 toward thedownstream side of a sheet conveyance direction. A feeding driven roller4 is biased against the feeding roller 3 to sandwich the printing sheet1 with the feeding roller 3, thereby feeding the printing sheet 1.

A conveyance roller 5 conveys the printing sheet 1 fed by the feedingroller 3 and feeding driven roller 4 to a position facing a printhead 7.A pinch roller 6 is biased against the conveyance roller 5 to sandwichthe printing sheet with the conveyance roller 5, thereby conveying theprinting sheet.

The printhead 7 prints the printing sheet 1 conveyed by the conveyanceroller 5 and pinch roller 6. In this embodiment, an inkjet printheadwhich prints the printing sheet 1 by discharging ink from the printheadwill be exemplified. A platen 8 supports the reverse surface of theprinting sheet 1 at the position facing the printhead 7. A carriage 10mounts the printhead 7 and moves in a direction intersecting the sheetconveyance direction.

A discharge roller 9 discharges the printing sheet printed by theprinthead 7 to the outside of the apparatus. Spurs 12 and 13 rotatewhile they are in contact with the printing surface of the printingsheet printed by the printhead 7. The spur 13 on the downstream side isbiased against the discharge roller 9, and no discharge roller 9 isarranged at a position facing the spur 12 on the upstream side. The spur12 is used to prevent the floating of the printing sheet 1, and is alsoreferred to as a pressing spur.

A conveyance guide 15 guides the printing sheet 1 between a feeding nipportion formed by the feeding roller 3 and feeding driven roller 4 and aconveyance nip portion formed by the conveyance roller 5 and pinchroller 6. A sheet detection sensor 16 detects the leading edge andtrailing edge of the printing sheet 1. The sheet detection sensor 16 isprovided downstream of the feeding roller 3 in the sheet conveyancedirection. A sheet pressing lever 17 makes the leading edge of thesucceeding sheet overlap the trailing edge of the preceding sheet. Thesheet pressing lever 17 is biased by a spring around a rotating shaft 17b in a counterclockwise direction in FIG. 1.

FIGS. 4A and 4B are views for explaining the arrangement of the pickuproller 2. As described above, the pickup roller 2 abuts against the topprinting sheet stacked on the feeding tray 11 to pick it up. A drivingshaft 19 transmits driving of a feeding motor (to be described later) tothe pickup roller 2. When picking up the printing sheet, the drivingshaft 19 and the pickup roller 2 rotate in a direction indicated by anarrow A in FIGS. 4A and 4B. A projection 19 a is formed in the drivingshaft 19. A concave portion 2 c in which the projection 19 a fits isformed in the pickup roller 2. As shown in FIG. 4A, when the projection19 a abuts against a first surface 2 a of the concave portion 2 c of thepickup roller 2, driving of the driving shaft 19 is transmitted to thepickup roller 2. In this case, when the driving shaft 19 is driven, thepickup roller 2 is also rotated. On the other hand, as shown in FIG. 4B,when the projection 19 a abuts against a second surface 2 b of theconcave portion 2 c of the pickup roller 2, driving of the driving shaft19 is not transmitted to the pickup roller 2. In this case, even if thedriving shaft 19 is driven, the pickup roller 2 is not rotated. Also,when the projection 19 a is formed between the first surface 2 a and thesecond surface 2 b without abutting against the first surface 2 a or thesecond surface 2 b, even if the driving shaft 19 is driven, the pickuproller 2 is not rotated.

FIG. 5 is a block diagram showing the printing apparatus according tothis embodiment. An MPU 201 controls the operation of each unit, dataprocessing, and the like. As will be described later, the MPU 201 alsofunctions as a conveyance control means capable of controllingconveyance of the printing sheets so that the trailing edge of apreceding sheet and the leading edge of a succeeding sheet overlap eachother. A ROM 202 stores data and programs to be executed by the MPU 201.A RAM 203 temporarily stores processing data to be executed by the MPU201 and data received from a host computer 214.

A printhead driver 207 controls the printhead 7. A carriage motor driver208 controls a carriage motor 204 for driving the carriage 10. Aconveyance motor 205 drives the conveyance roller 5 and discharge roller9. A conveyance motor driver 209 controls the conveyance motor 205. Afeeding motor 206 drives the pickup roller 2 and feeding roller 3. Afeeding motor driver 210 controls the feeding motor 206.

In the host computer 214, a printer driver 2141 is used to communicatewith the printing apparatus by collecting printing information such as aprinting image and printing image quality when the user instructs theexecution of a printing operation. The MPU 201 exchanges the printingimage and the like with the host computer 214 via an I/F unit 213.

The overlap continuous feeding operation will be described in timeseries with reference to ST1 to ST9 of FIGS. 1 to 3. When the hostcomputer 214 transmits printing data via the I/F unit 213, the printingdata is processed by the MPU 201, and then loaded into the RAM 203. TheMPU 201 starts a printing operation based on the loaded data.

A description will be provided with reference to ST1 of FIG. 1. Thefeeding motor driver 210 drives the feeding motor 206 at low speed. Thisrotates the pickup roller 2 (first feeding roller) at 7.6 inches/sec.When the pickup roller 2 rotates, the top printing sheet (a precedingsheet 1-A) stacked on the feeding tray 11 is picked up. The precedingsheet 1-A picked up by the pickup roller 2 is conveyed by the feedingroller 3 (a second feeding roller) rotating in the same direction asthat of the pickup roller 2. The feeding motor 206 also drives thefeeding roller 3.

When the sheet detection sensor 16 provided on the downstream side ofthe feeding roller 3 detects the leading edge of the preceding sheet1-A, the feeding motor 206 is switched to high-speed driving. That is,the pickup roller 2 and feeding roller 3 rotate at 20 inches/sec.

A description will be provided with reference to ST2 of FIG. 1. When thefeeding roller 3 is continuously rotated, the leading edge of thepreceding sheet 1-A rotates the sheet pressing lever 17 about therotating shaft 17 b in the clockwise direction against the biasing forceof the spring. When the feeding roller 3 is further continuouslyrotated, the leading edge of the preceding sheet 1-A abuts against theconveyance nip portion formed by the conveyance roller 5 and pinchroller 6. At this time, the conveyance roller 5 stops. By rotating thefeeding roller 3 by a predetermined amount even after the leading edgeof the preceding sheet 1-A abuts against the conveyance nip portion,alignment of the preceding sheet 1-A is performed to correct the skewwhile the leading edge of the preceding sheet 1-A abuts against theconveyance nip portion. The skew correction operation will also bereferred to as a registration adjustment operation.

A description will be provided with reference to ST3 of FIG. 1. Upon endof the skew correction operation of the preceding sheet 1-A, theconveyance motor 205 is driven to start rotation of the conveyanceroller 5. The conveyance roller 5 conveys the sheet at 15 inches/sec.After the preceding sheet 1-A is aligned with the position facing theprinthead 7, a printing operation is performed by discharging ink fromthe printhead 7 based on the printing data. Note that the alignmentoperation is performed by making the leading edge of the printing sheetabut against the conveyance nip portion to temporarily position theprinting sheet at the position of the conveyance roller 5, andcontrolling the rotation amount of the conveyance roller 5 withreference to the position of the conveyance roller 5.

The printing apparatus of this embodiment is a serial type printingapparatus in which the carriage 10 mounts the printhead 7. An operationof printing the printing sheet is performed by repeating a conveyanceoperation of intermittently conveying the printing sheet by apredetermined amount using the conveyance roller 5 and an image formingoperation of discharging ink from the printhead 7 while moving thecarriage 10 incorporating the printhead 7 when the conveyance roller 5stops.

When alignment of the preceding sheet 1-A is performed, the feedingmotor 206 is switched to low-speed driving. That is, the pickup roller 2and feeding roller 3 rotate at 7.6 inches/sec. While the conveyanceroller 5 intermittently conveys the printing sheet by the predeterminedamount, the feeding motor 206 also intermittently drives the feedingroller 3. That is, while the conveyance roller 5 rotates, the feedingroller 3 also rotates. While the conveyance roller 5 stops, the feedingroller 3 also stops. The rotation speed of the feeding roller 3 is lowerthan that of the conveyance roller 5. Consequently, the sheet isstretched between the conveyance roller 5 and the feeding roller 3. Thefeeding roller 3 is rotated together with the printing sheet conveyed bythe conveyance roller 5.

Since the feeding motor 206 is intermittently driven, the driving shaft19 is also driven. As described above, the rotation speed of the pickuproller 2 is lower than that of the conveyance roller 5. Consequently,the pickup roller 2 is rotated together with the printing sheet conveyedby the conveyance roller 5. That is, the pickup roller 2 rotates aheadof the driving shaft 19. More specifically, the projection 19 a of thedriving shaft 19 is spaced apart from the first surface 2 a and abutsagainst the second surface 2 b. Therefore, the second printing sheet (asucceeding sheet 1-B) is not picked up soon after the trailing edge ofthe preceding sheet 1-A passes through the pickup roller 2. After thedriving shaft 19 is driven for a predetermined time, the projection 19 aabuts against the first surface 2 a and the pickup roller 2 starts torotate.

A description will be provided with reference to ST4 of FIG. 2. In ST4,a state in which the pickup roller 2 starts to rotate, and picks up thesucceeding sheet 1-B is shown. Due to a factor such as theresponsiveness of the sensor, the sheet detection sensor 16 requires apredetermined interval or more between the printing sheets to detect theedges of the printing sheets. That is, it is necessary to separate theleading edge of the succeeding sheet 1-B from the trailing edge of thepreceding sheet 1-A by a predetermined distance to provide apredetermined time interval from when the sheet detection sensor 16detects the trailing edge of the preceding sheet 1-A until it detectsthe leading edge of the succeeding sheet 1-B. To achieve this, the angleof the concave portion 2 c of the pickup roller 2 is set to about 70°.

A description will be provided with reference to ST5 of FIG. 2. Thesucceeding sheet 1-B picked up by the pickup roller 2 is conveyed by thefeeding roller 3. At this time, the preceding sheet 1-A undergoes animage forming operation by the printhead 7 based on the printing data.When the sheet detection sensor 16 detects the leading edge of thesucceeding sheet 1-B, the feeding motor 206 is switched to high-speeddriving. That is, the pickup roller 2 and feeding roller 3 rotate at 20inches/sec.

A description will be provided with reference to ST6 of FIG. 2. Thesheet pressing lever 17 presses the trailing edge of the preceding sheet1-A downward, as shown in ST5 of FIG. 2. It is possible to form a statein which the leading edge of the succeeding sheet 1-B overlaps thetrailing edge of the preceding sheet 1-A by moving the succeeding sheet1-B at a speed higher than that at which the preceding sheet 1-A movesdownstream by the printing operation of the printhead 7 (ST6 of FIG. 2).Since the preceding sheet 1-A undergoes the printing operation based onthe printing data, it is intermittently conveyed by the conveyanceroller 5. On the other hand, after the sheet detection sensor 16 detectsthe leading edge of the succeeding sheet 1-B, the succeeding sheet 1-Bcan catch up with the preceding sheet 1-A by continuously rotating thefeeding roller 3 at 20 inches/sec.

A description will be provided with reference to ST7 of FIG. 3. Afterforming an overlap state in which the leading edge of the succeedingsheet 1-B overlaps the trailing edge of the preceding sheet 1-A, thesucceeding sheet 1-B is conveyed by the feeding roller 3 until theleading edge of the succeeding sheet 1-B stops at a predeterminedposition upstream of the conveyance nip portion. The position of theleading edge of the succeeding sheet 1-B is calculated from the rotationamount of the feeding roller 3 after the sheet detection sensor 16detects the leading edge of the succeeding sheet 1-B, and controlledbased on the calculation result. At this time, the preceding sheet 1-Aundergoes an image forming operation based on the printing data by theprinthead 7.

A description will be provided with reference to ST8 of FIG. 3. When theconveyance roller 5 stops to perform the image forming operation (inkdischarge operation) of the last row of the preceding sheet 1-A, thefeeding roller 3 is driven to make the leading edge of the printingsheet 1-B abut against the conveyance nip portion, thereby performingthe skew correction operation of the succeeding sheet 1-B.

A description will be provided with reference to ST9 of FIG. 3. When theimage forming operation of the last row of the preceding sheet 1-A ends,it is possible to perform alignment of the succeeding sheet 1-B whilekeeping the state in which the succeeding sheet 1-B overlaps thepreceding sheet 1-A by rotating the conveyance roller 5 by apredetermined amount. The succeeding sheet 1-B undergoes a printingoperation by the printhead 7 based on the printing data. When thesucceeding sheet 1-B is intermittently conveyed for the printingoperation, the preceding sheet 1-A is also intermittently conveyed, andis finally discharged outside the printing apparatus by the dischargeroller 9.

When alignment of the succeeding sheet 1-B is performed, the feedingmotor 206 is switched to low-speed driving. That is, the pickup roller 2and feeding roller 3 rotate at 7.6 inches/sec. If there is printing dataeven after the succeeding sheet 1-B, the process returns to ST4 of FIG.2 to pick up the third printing sheet.

FIGS. 6A and 6B are flowcharts illustrating the overlap continuousfeeding operation according to this embodiment. In step S1, when thehost computer 214 transmits printing data via the I/F unit 213, aprinting operation starts. In step S2, the feeding operation of thepreceding sheet 1-A starts. More specifically, the feeding motor 206 isdriven at low speed. The pickup roller 2 rotates at 7.6 inches/sec. Thepickup roller 2 picks up the preceding sheet 1-A, and the feeding roller3 feeds the preceding sheet 1-A toward the printhead 7.

In step S3, the sheet detection sensor 16 detects the leading edge ofthe preceding sheet 1-A. When the sheet detection sensor 16 detects theleading edge of the preceding sheet 1-A, the feeding motor 206 isswitched to high-speed driving in step S4. That is, the pickup roller 2and feeding roller 3 rotate at 20 inches/sec. In step S5, by controllingthe rotation amount of the feeding roller 3 after the sheet detectionsensor 16 detects the leading edge of the preceding sheet 1-A, theleading edge of the preceding sheet 1-A is made to abut against theconveyance nip portion to perform the skew correction operation of thepreceding sheet 1-A.

In step S6, alignment of the preceding sheet 1-A is performed based onthe printing data. That is, the preceding sheet 1-A is conveyed to aprinting start position with reference to the position of the conveyanceroller 5 based on the printing data by controlling the rotation amountof the conveyance roller 5. In step S7, the feeding motor 206 isswitched to low-speed driving. In step S8, a printing operation startswhen the printhead 7 discharges ink to the preceding sheet 1-A. Morespecifically, the printing operation of the preceding sheet 1-A isperformed by repeating a conveyance operation of intermittentlyconveying the preceding sheet 1-A by the conveyance roller 5 and animage forming operation (ink discharge operation) of discharging inkfrom the printhead 7 by moving the carriage 10. The feeding motor 206 isintermittently driven at low speed in synchronization with the operationof intermittently conveying the preceding sheet 1-A by the conveyanceroller 5. That is, the pickup roller 2 and feeding roller 3intermittently rotate at 7.6 inches/sec.

In step S9, it is determined whether there is printing data of the nextpage. If there is no printing data of the next page, the processadvances to step S25. Upon completion of the printing operation of thepreceding sheet 1-A in step S25, the preceding sheet 1-A is dischargedin step S26, thereby terminating the printing operation.

If there is printing data of the next page, the feeding operation of thesucceeding sheet 1-B starts in step S10. More specifically, the pickuproller 2 picks up the succeeding sheet 1-B, and the feeding roller 3feeds the succeeding sheet 1-B toward the printhead 7. The pickup roller2 rotates at 7.6 inches/sec. As described above, since the large concaveportion 2 c of the pickup roller 2 is provided with respect to theprojection 19 a of the driving shaft 19, the succeeding sheet 1-B is fedwhile having a predetermined interval with respect to the trailing edgeof the preceding sheet 1-A.

In step S11, the sheet detection sensor 16 detects the leading edge ofthe succeeding sheet 1-B. When the sheet detection sensor 16 detects theleading edge of the succeeding sheet 1-B, the feeding motor 206 isswitched to high-speed driving in step S12. That is, the pickup roller 2and feeding roller 3 rotate at 20 inches/sec. In step S13, bycontrolling the rotation amount of the feeding roller 3 after the sheetdetection sensor 16 detects the leading edge of the succeeding sheet1-B, the succeeding sheet 1-B is conveyed so that its leading edge is ata position a predetermined amount before the conveyance nip portion. Thepreceding sheet 1-A is intermittently conveyed based on the printingdata. Continuously driving the feeding motor 206 at high speed forms theoverlap state in which the leading edge of the succeeding sheet 1-Boverlaps the trailing edge of the preceding sheet 1-A.

In step S14, it is determined whether predetermined conditions (to bedescribed later) are satisfied. If the predetermined conditions aresatisfied, it is determined in step S15 whether the image formingoperation of the preceding sheet 1-A has started. If it is determinedthat the image forming operation has started, the process advances tostep S16; otherwise, the process stands by until the image formingoperation starts. In step S16, the leading edge of the succeeding sheet1-B is made to abut against the conveyance nip portion while keeping theoverlap state, thereby performing the skew correction operation of thesucceeding sheet 1-B. If it is determined in step S17 that the imageforming operation of the last row of the preceding sheet 1-A has ended,in step S18 alignment of the succeeding sheet 1-B is performed whilekeeping the overlap state.

If it is determined in step S14 that the predetermined conditions arenot satisfied, the overlap state is canceled to perform alignment of thesucceeding sheet 1-B. More specifically, if it is determined in step S27that the image forming operation of the last row of the preceding sheet1-A has ended, the discharge operation of the preceding sheet 1-A isperformed in step S28. During this operation, the feeding motor 206 isnot driven, and thus the succeeding sheet 1-B stops while its leadingedge is at the position the predetermined amount before the conveyancenip portion. Since the preceding sheet 1-A is discharged, the overlapstate is canceled. In step S29, the leading edge of the succeeding sheet1-B is made to abut against the conveyance nip portion to perform theskew correction operation of the succeeding sheet 1-B. In step S18,alignment of the succeeding sheet 1-B is performed.

In step S19, the feeding motor 206 is switched to low-speed driving. Instep S20, a printing operation starts by discharging ink from theprinthead 7 to the succeeding sheet 1-B. More specifically, the printingoperation of the succeeding sheet 1-B is performed by repeating(performing printing control) a conveyance operation of intermittentlyconveying the succeeding sheet 1-B by the conveyance roller 5 and animage forming operation (ink discharge operation) of discharging inkfrom the printhead 7 by moving the carriage 10. The feeding motor 206 isintermittently driven at low speed in synchronization with the operationof intermittently conveying the succeeding sheet 1-B by the conveyanceroller 5. That is, the pickup roller 2 and feeding roller 3intermittently rotate at 7.6 inches/sec.

In step S21, it is determined whether there is printing data of the nextpage. If there is printing data of the next page, the process returns tostep S10. If there is no printing data of the next page, when the imageforming operation of the succeeding sheet 1-B is complete in step S22,the discharge operation of the succeeding sheet 1-B is performed in stepS23 and the printing operation ends in step S24.

FIGS. 7 and 8 are views for explaining an operation of making asucceeding sheet overlap a preceding sheet according to this embodiment.The operation of forming the overlap state in which the leading edge ofthe succeeding sheet overlaps the trailing edge of the preceding sheet,which has been explained in steps S12 and S13 of FIG. 6, will bedescribed.

FIGS. 7 and 8 are enlarged views each showing a portion between thefeeding nip portion formed by the feeding roller 3 and feeding drivenroller 4 and the conveyance nip portion formed by the conveyance roller5 and pinch roller 6.

Three states in a process of conveying the printing sheets by theconveyance roller 5 and feeding roller 3 will be sequentially described.The first state in which an operation of making the succeeding sheetchase the preceding sheet is performed will be described with referenceto ST1 and ST2 of FIG. 7. The second state in which an operation ofmaking the succeeding sheet overlap the preceding sheet is performedwill be described with reference to ST3 and ST4 of FIG. 8. The thirdstate in which it is determined whether to perform the skew correctionoperation of the succeeding sheet while keeping the overlap state willbe described with reference to ST5 of FIG. 8.

In ST1 of FIG. 7, the feeding roller 3 is controlled to convey thesucceeding sheet 1-B, and the sheet detection sensor 16 detects theleading edge of the succeeding sheet 1-B. A section from the sheetdetection sensor 16 to a position P1 at which the succeeding sheet 1-Bcan be made to overlap the preceding sheet 1-A is defined as a firstsection A1. In the first section A1, an operation of making the leadingedge of the succeeding sheet 1-B chase the trailing edge of thepreceding sheet 1-A is performed. The position P1 is decided based onthe arrangement of the mechanism.

In the first state, the chasing operation may stop in the first sectionA1. If, as shown in ST2 of FIG. 7, the leading edge of the succeedingsheet 1-B passes the trailing edge of the preceding sheet 1-A before theposition P1, the operation of making the succeeding sheet overlap thepreceding sheet is not performed.

In ST3 of FIG. 8, a section from the above-described position P1 to aposition P2 at which the sheet pressing lever 17 is provided is definedas a second section A2. In the second section A2, the operation ofmaking the succeeding sheet 1-B overlap the preceding sheet 1-A isperformed.

In the second state, the operation of making the succeeding sheetoverlap the preceding sheet may stop in the second section A2. If, asshown in ST4 of FIG. 8, the leading edge of the succeeding sheet 1-Bcannot catch up with the trailing edge of the preceding sheet 1-A withinthe second section A2, it is impossible to perform the operation ofmaking the succeeding sheet overlap the preceding sheet.

In ST5 of FIG. 8, a section from the above-described position P2 to aposition P3 is defined as a third section A3. The position P3 is theposition of the leading edge of the succeeding sheet when the succeedingsheet stops in step S13 of FIG. 6. While the succeeding sheet 1-Boverlaps the preceding sheet 1-A, the succeeding sheet 1-B is conveyedso that its leading edge reaches the position P3. In the third sectionA3, it is determined whether to perform alignment of the succeedingsheet 1-B by making it abut against the conveyance nip portion whilekeeping the overlap state. That is, it is determined whether to performalignment of the succeeding sheet by executing a skew correctionoperation while keeping the overlap state or to perform alignment of thesucceeding sheet by canceling the overlap state and performing a skewcorrection operation.

FIG. 9 is a flowchart for explaining the skew correction operation ofthe succeeding sheet according to this embodiment. The processing ofdetermining whether the predetermined conditions are satisfied, whichhas been explained in step S14 of FIG. 6, will be described in detail.

The operation of determining whether to perform a skew correctionoperation by making the leading edge of the succeeding sheet 1-B abutagainst the conveyance nip portion while keeping the overlap statebetween the preceding sheet 1-A and the succeeding sheet 1-B or toperform a skew correction operation by canceling the overlap statebetween the preceding sheet 1-A and the succeeding sheet 1-B and thenmaking the leading edge of the succeeding sheet 1-B abut against theconveyance nip portion will be described.

In step S101, the operation starts. In step S102, it is determinedwhether the leading edge of the succeeding sheet 1-B has reached thedetermination position (the position P3 in ST5 of FIG. 8). If theleading edge of the succeeding sheet 1-B has not reached thedetermination position (NO in step S102), it is uncertain whether theleading edge of the succeeding sheet 1-B abuts against the conveyancenip portion by conveying the succeeding sheet 1-B by a predeterminedamount, and thus a skew correction operation for only the succeedingsheet is decided (step S103), thereby terminating the determinationoperation (step S104). That is, after the trailing edge of the precedingsheet 1-A passes through the conveyance nip portion, only the succeedingsheet 1-B is made to abut against the conveyance nip portion to performa skew correction operation, and then alignment of only the succeedingsheet 1-B is performed.

On the other hand, if it is determined that the succeeding sheet 1-B hasreached the determination position P3 (YES in step S102), it isdetermined whether the trailing edge of the preceding sheet 1-A haspassed through the conveyance nip portion (step S105). If it isdetermined that the trailing edge of the preceding sheet 1-A has passedthrough the conveyance nip portion (YES in step pS105), the succeedingsheet does not overlap the preceding sheet, and thus a skew correctionoperation for only the succeeding sheet is decided (step S106). That is,only the succeeding sheet 1-B is made to abut against the conveyance nipportion to perform a skew correction operation, and then alignment ofonly the succeeding sheet 1-B is performed.

On the other hand, if it is determined that the trailing edge of thepreceding sheet 1-A has not passed through the conveyance nip portion(NO in step S105), it is determined whether the overlap amount of thetrailing edge of the preceding sheet 1-A and the leading edge of thesucceeding sheet 1-B is smaller than a threshold (step S107). Theposition of the trailing edge of the preceding sheet 1-A is updatedalong with the printing operation of the preceding sheet 1-A. Theposition of the leading edge of the succeeding sheet 1-B is at theabove-described determination position. That is, the overlap amountdecreases along with the printing operation of the preceding sheet 1-A.If it is determined that the overlap amount is smaller than thethreshold (YES in step S107), the overlap state is canceled, and a skewcorrection operation for only the succeeding sheet is decided (stepS108). That is, after the image forming operation of the preceding sheet1-A ends, the succeeding sheet 1-B is not conveyed together with thepreceding sheet 1-A. More specifically, the conveyance motor 205 drivesthe conveyance roller 5 to convey the preceding sheet 1-A. However, thefeeding roller 3 is not driven. Therefore, the overlap state iscanceled. Furthermore, only the succeeding sheet 1-B is made to abutagainst the conveyance nip portion to perform a skew correctionoperation, and then alignment of only the succeeding sheet 1-B isperformed.

If it is determined that the overlap amount is equal to or larger thanthe threshold (NO in step S107), it is determined whether the succeedingsheet 1-B reaches the pressing spur 12 when alignment of the succeedingsheet 1-B is performed (step S109). If it is determined that thesucceeding sheet 1-B does not reach the pressing spur 12 (NO in stepS109), the overlap state is canceled and a skew correction operation foronly the succeeding sheet is decided (step S110). That is, after theimage forming operation of the preceding sheet 1-A ends, the succeedingsheet 1-B is not conveyed together with the preceding sheet 1-A. Morespecifically, the conveyance motor 205 drives the conveyance roller 5 toconvey the preceding sheet 1-A. However, the feeding roller 3 is notdriven. Consequently, the overlap state is canceled. Furthermore, onlythe succeeding sheet 1-B is made to abut against the conveyance nipportion to perform a skew correction operation, and then alignment ofonly the succeeding sheet 1-B is performed.

If it is determined that the succeeding sheet 1-B reaches the pressingspur 12 (YES in step S109), it is determined whether there is a gapbetween the last row of the preceding sheet and the row immediatelypreceding the last row (step S111). If it is determined that there is nogap (NO in step S111), the overlap state is canceled and a skewcorrection operation for only the succeeding sheet is decided (stepS112). If it is determined that there is a gap (YES in step S111), theskew correction operation of the succeeding sheet 1-B is performed whilekeeping the overlap state, and alignment of the succeeding sheet 1-B isperformed. That is, after the image forming operation of the precedingsheet 1-A ends, the succeeding sheet 1-B is made to abut against theconveyance nip portion while overlapping the preceding sheet 1-A. Morespecifically, the conveyance roller 5 and the feeding roller 3 arerotated by driving the feeding motor 206 together with the conveyancemotor 205. After the skew correction operation, alignment of thesucceeding sheet 1-B is performed while the succeeding sheet 1-Boverlaps the preceding sheet 1-A.

As described above, the operation of determining whether to keep orcancel the overlap state between the preceding sheet 1-A and thesucceeding sheet 1-B is performed.

FIG. 10 is a flowchart for explaining an arrangement of calculating theleading edge position of the succeeding sheet after alignment of thesucceeding sheet according to this embodiment.

In step S201, the process starts. In step S202, a printable area with asheet size is loaded. Since the uppermost printable position, that is,the upper end margin is specified, the upper end margin of the printablearea is set as a leading edge position (step S203). Note that theleading edge position is defined by the distance from the conveyance nipportion.

The first printing data is loaded (step S204). With this processing, theposition of the first printing data from the leading edge of the sheetis specified, and thus it is determined whether the distance between theleading edge of the sheet and the first printing data is larger than thepreviously set leading edge position (step S205). If the distancebetween the leading edge of the sheet and the first printing data islarger than the previously set leading edge position (YES in step S205),the leading edge position is updated by the distance between the leadingedge of the sheet and the first printing data (step S206). If thedistance between the leading edge of the sheet and the first printingdata is equal to or smaller than the previously set leading edgeposition (NO in step S205), the process advances to step S207.

Next, the first carriage movement instruction is generated (step S207).It is determined whether a sheet conveyance amount for the firstcarriage movement is larger than the previously set leading edgeposition (step S208). If the sheet conveyance amount for the firstcarriage movement is larger than the previously set leading edgeposition (YES in step S208), the leading edge position is updated by thesheet conveyance amount for the first carriage movement (step S209). Ifthe sheet conveyance amount for the first carriage movement is equal toor smaller than the previously set leading edge position (NO in stepS208), the leading edge position is not updated. In this manner, theleading edge position of the succeeding sheet 1-B is confirmed (stepS210), and the process ends (step S211).

As described above, according to the above embodiment, by determiningwhether to convey the succeeding sheet to the position facing theprinthead 7 while keeping the overlap state when the leading edge of thesucceeding sheet 1-B is made to overlap the trailing edge of thepreceding sheet 1-A, it is possible to start to feed the succeedingsheet even if the marginal amount of the trailing edge of the precedingsheet 1-A and that of the leading edge of the succeeding sheet are notconfirmed.

When performing the printing operation of the preceding sheet 1-A by theprinthead 7, the feeding motor 206 is driven in synchronization with theconveyance motor 205 before the sheet detection sensor 16 detects theleading edge of the succeeding sheet 1-B, and the feeding motor 206 iscontinuously driven after the sheet detection sensor 16 detects theleading edge of the succeeding sheet, thereby making it possible toperform a chasing operation to make the succeeding sheet overlap thepreceding sheet.

Second Embodiment

A printing apparatus according to the second embodiment of the presentinvention will be described next. In the first embodiment, the serialtype printing apparatus in which the carriage 10 mounts the printhead 7has been explained. To the contrary, in the second embodiment, a linetype printhead 20 is used, in which inkjet nozzle array is formed withina range covering the maximum width of sheets, as shown in FIGS. 11A to11C.

The line type printhead 20 performs, from above, print processing on asheet conveyed by a conveyance roller 5 like the serial type printingapparatus, thereby forming an image. However, since no carriage movementoperation is performed, the stop time of the conveyance roller 5 becomesunnecessary.

In the line type printhead 20, a plurality of printheads are arranged inparallel along the sheet conveyance direction. In this embodiment, theline type printhead 20 includes printheads corresponding to four colorsof C (cyan), M (magenta), Y (yellow), and K (black). Note that each ofthe number of colors and the number of printheads is not limited tofour. The respective color inks are supplied from ink tanks (not shown)to the respective color nozzles of the line type printhead 20 via inktubes.

The same operation as in the first embodiment is performed until apickup roller 2 picks up a preceding sheet 1-A, the conveyance roller 5conveys it, and thus alignment of the preceding sheet 1-A is performed.After alignment of the preceding sheet 1-A is performed, the precedingsheet 1-A is continuously conveyed by the conveyance roller 5.

Note that when alignment of the preceding sheet 1-A ends, a feedingmotor 206 is switched to low-speed driving in step S7 of FIG. 6. Withthis processing, the pickup roller 2 and a feeding roller 3 rotate at7.6 inches/sec.

If it is determined in step S9 of FIG. 6 that there is printing data ofthe next page, the feeding operation of a succeeding sheet 1-B starts instep S10. As described in the first embodiment, the succeeding sheet isfed while having a predetermined interval with respect to the trailingedge of the preceding sheet.

If a sheet detection sensor 16 detects the leading edge of thesucceeding sheet 1-B in step S11, the feeding motor 206 is switched tohigh-speed driving in step S12. The preceding sheet 1-A is printed basedon printing data while being continuously conveyed, as described above.On the other hand, the feeding roller 3 conveys the succeeding sheet 1-Bat a speed higher than the conveying speed of the preceding sheet 1-A bythe conveyance roller 5, for example, at 20 inches/sec. Consequently, itis possible to form a state in which the leading edge of the succeedingsheet 1-B overlaps the trailing edge of the preceding sheet 1-A.

In the image forming operation by the line type printhead 20, there isno stop time of the conveyance roller 5 for the image forming operationof the last row. Therefore, when performing the skew correctionoperation of the succeeding sheet, the conveyance operation of thepreceding sheet is temporarily stopped. By providing such stop time, inthe line type printhead 20 as well, it is possible to perform a skewcorrection operation while the succeeding sheet overlaps the precedingsheet after performing the chasing operation and overlap operation ofthe preceding sheet and succeeding sheet.

Other Embodiments

Embodiment(s) of the present invention can also be realized by acomputer of a system or apparatus that reads out and executes computerexecutable instructions (e.g., one or more programs) recorded on astorage medium (which may also be referred to more fully as a‘non-transitory computer-readable storage medium’) to perform thefunctions of one or more of the above-described embodiment(s) and/orthat includes one or more circuits (e.g., application specificintegrated circuit (ASIC)) for performing the functions of one or moreof the above-described embodiment(s), and by a method performed by thecomputer of the system or apparatus by, for example, reading out andexecuting the computer executable instructions from the storage mediumto perform the functions of one or more of the above-describedembodiment(s) and/or controlling the one or more circuits to perform thefunctions of one or more of the above-described embodiment(s). Thecomputer may comprise one or more processors (e.g., central processingunit (CPU), micro processing unit (MPU)) and may include a network ofseparate computers or separate processors to read out and execute thecomputer executable instructions. The computer executable instructionsmay be provided to the computer, for example, from a network or thestorage medium. The storage medium may include, for example, one or moreof a hard disk, a random-access memory (RAM), a read only memory (ROM),a storage of distributed computing systems, an optical disk (such as acompact disc (CD), digital versatile disc (DVD), or Blu-ray Disc (BD)™),a flash memory device, a memory card, and the like.

While the present invention has been described with reference toexemplary embodiments, it is to be understood that the invention is notlimited to the disclosed exemplary embodiments. The scope of thefollowing claims is to be accorded the broadest interpretation so as toencompass all such modifications and equivalent structures andfunctions.

This application claims the benefit of Japanese Patent Application No.2014-046762, filed Mar. 10, 2014, which is hereby incorporated byreference herein in its entirety.

What is claimed is:
 1. A printing apparatus comprising: a first rollerconfigured to feed a sheet; a second roller configured to convey thesheet fed by the first roller; a third roller configured to convey thesheet conveyed by the second roller; a printhead configured to print animage by discharging ink on the sheet; and a conveyance control unitconfigured to control conveyance of the sheet, wherein the third rollerperforms intermittent driving which is repeating conveyance of the sheetand stopping conveyance of the sheet, and the printhead prints on thesheet in a state in which the third roller stops the conveyance of thesheet, wherein the conveyance control unit controls the first roller tofeed a succeeding sheet so as to have an interval between a trailingedge of a preceding sheet fed before the succeeding sheet and a leadingedge of the succeeding sheet, and wherein the conveyance control unitcontrols the second roller to perform intermittent driving in a statewhere the third roller performs the intermittent driving for printing onthe preceding sheet and the preceding sheet is conveyed by the secondroller, and controls the second roller to convey the succeeding sheet ina state where the third roller stops the conveyance of the precedingsheet in the intermittent driving after the trailing edge of thepreceding sheet passes the second roller.
 2. The apparatus according toclaim 1, wherein in a state in which the conveyance of the precedingsheet stops, the conveyance control unit performs skew correction of thesucceeding sheet by causing the succeeding sheet to abut against thethird roller.
 3. The apparatus according to claim 1, wherein a conveyingspeed of the succeeding sheet by the second roller in a state where thethird roller stops the conveyance of the preceding sheet in theintermittent driving after the trailing edge of the preceding sheetpasses the second roller is set to a speed higher than a conveying speedof the preceding sheet by the third roller.
 4. The apparatus accordingto claim 1, wherein the conveyance control unit causes the leading edgeof the succeeding sheet to overlap the preceding sheet between thesecond roller and the third roller.
 5. The apparatus according to claim1, wherein, in a case that the second roller performs intermittentdriving, the conveyance control unit does not form an overlap state inwhich the leading edge of the succeeding sheet is overlapping with thepreceding sheet, and in a case that the second roller conveys thesucceeding sheet in a state where the third roller stops the conveyanceof the preceding sheet in the intermittent driving after the trailingedge of the preceding sheet passes the second roller, the conveyancecontrol unit forms the overlap state between the second roller and thethird roller.
 6. The apparatus according to claim 5, wherein theconveyance control unit conveys the succeeding sheet to a positionfacing the printhead while keeping the overlap state in a case that theconveyance control unit forms the overlap state.
 7. The apparatusaccording to claim 1, wherein the conveyance control unit, after thetrailing edge of the preceding sheet passes the second roller,continuously drives the second roller such that a conveyance amount ofthe succeeding sheet conveyed by the second roller during apredetermined time period is greater than a conveyance amount of thepreceding sheet conveyed by the third roller during the predeterminedtime period.
 8. The apparatus according to claim 1, wherein theconveyance control unit, after the trailing edge of the preceding sheetpasses the second roller, stops the driving of the second roller afterthe leading edge of the succeeding sheet reaches a predeterminedposition.
 9. The apparatus according to claim 8, wherein the conveyancecontrol unit, after the driving of the second roller is stopped,performs a skew correction of the succeeding sheet by causing thesucceeding sheet to abut against the third roller in a state where thethird roller stops the conveyance of the preceding sheet in theintermittent driving.
 10. The apparatus according to claim 9, whereinthe conveyance control unit performs the skew correction of thesucceeding sheet in a state in which the leading edge of the succeedingsheet is overlapping with the preceding sheet.
 11. The apparatusaccording to claim 10, wherein the conveyance control unit conveys thesucceeding sheet to a printing start position at which the printingoperation is started by the printhead while keeping the overlap state.12. A method of controlling a printing apparatus including a firstroller configured to feed a sheet, a second roller configured to conveythe sheet fed by the first roller, a third roller configured to conveythe sheet conveyed by the second roller, and a printhead configured toprint an image by discharging ink on the sheet, wherein the third rollerperforms intermittent driving which is repeating conveyance of the sheetand stopping conveyance of the sheet, and the printhead prints on thesheet in a state in which the third roller stops the conveyance of thesheet, the method comprising: controlling the first roller to feed asucceeding sheet so as to have an interval between a trailing edge of apreceding sheet fed before the succeeding sheet and a leading edge ofthe succeeding sheet; controlling the second roller to performintermittent driving in a state where the third roller performs theintermittent driving for printing on the preceding sheet and thepreceding sheet is conveyed by the second roller; and controlling thesecond roller to convey the succeeding sheet in a state where the thirdroller stops the conveyance of the preceding sheet in the intermittentdriving after the trailing edge of the preceding sheet passes the secondroller.
 13. The method according to claim 12, further comprisingperforming skew correction of the succeeding sheet by causing thesucceeding sheet to abut against the third roller in a case that theconveyance of the preceding sheet stops.
 14. The method according toclaim 12, wherein a conveying speed of the succeeding sheet by thesecond roller in a state where the third roller stops the conveyance ofthe preceding sheet in the intermittent driving after the trailing edgeof the preceding sheet passes the second roller is set to a speed higherthan a conveying speed of the preceding sheet by the third roller. 15.The method according to claim 12, further comprising forming an overlapstate in which the leading edge of the succeeding sheet is overlappingwith the preceding sheet between the second roller and the third rollerin a case that the second roller conveys the succeeding sheet in a statewhere the third roller stops the conveyance of the preceding sheet inthe intermittent driving after the trailing edge of the preceding sheetpasses the second roller.
 16. The method according to claim 15, furthercomprising conveying the succeeding sheet to a position facing theprinthead while keeping the overlap state after forming the overlapstate.
 17. The method according to claim 12, further comprising drivingthe second roller such that a conveyance amount of the succeeding sheetconveyed by the second roller during a predetermined time period isgreater than a conveyance amount of the preceding sheet conveyed by thethird roller during the predetermined time period.
 18. The methodaccording to claim 12, further comprising stopping the driving of thesecond roller after the leading edge of the succeeding sheet reaches apredetermined position.
 19. The method according to claim 18, furthercomprising performing a skew correction of the succeeding sheet bycausing the succeeding sheet to abut against the third roller in a statewhere the third roller stops the conveyance of the preceding sheet inthe intermittent driving.
 20. The method according to claim 19, whereinthe skew correction of the succeeding sheet is performed in a state inwhich the leading edge of the succeeding sheet is overlapping with thepreceding sheet.
 21. The method according to claim 20, furthercomprising conveying the succeeding sheet to a printing start positionat which the printing operation is started by the printhead whilekeeping the overlap state.
 22. A printing apparatus comprising: a firstroller configured to convey a sheet; a second roller configured toconvey the sheet conveyed by the first roller; a printing unitconfigured to print on the sheet conveyed by the second roller; and aconveyance control unit configured to control conveying the sheet,wherein the conveyance control unit controls conveying a succeedingsheet so as to have an interval between a trailing edge of a precedingsheet conveyed before the succeeding sheet and a leading edge of thesucceeding sheet, and wherein the conveyance control unit controls todrive the first roller in synchronization with driving of the secondroller in a state where the printing unit prints on the preceding sheetand the preceding sheet is conveyed by the first roller, and to drivethe first roller not in synchronization with driving of the secondroller so as to make the succeeding sheet catch up with the precedingsheet in a state where the printing unit prints on the preceding sheetafter the trailing edge of the preceding sheet passes the first roller.23. The printing apparatus according to claim 22, wherein the conveyancecontrol unit controls to drive the first roller not in synchronizationwith driving of the second roller so as to make the succeeding sheetoverlap with the preceding sheet.
 24. The printing apparatus accordingto claim 23, wherein the conveyance control unit controls to drive thesecond roller to convey the succeeding sheet to a position facing theprinting unit in a state in which the succeeding sheet overlaps with thepreceding sheet.
 25. The printing apparatus according to claim 24,wherein the printing unit includes a printhead configured to ejectliquid on the sheet.
 26. A method of controlling a printing apparatusincluding a first roller configured to convey a sheet, a second rollerconfigured to convey the sheet conveyed by the first roller, and aprinting unit configured to print on the sheet conveyed by the secondroller, the method comprising: conveying a succeeding sheet so as tohave an interval between a trailing edge of a preceding sheet conveyedbefore the succeeding sheet and a leading edge of the succeeding sheet;and controlling to drive the first roller in synchronization withdriving of the second roller in a state where the printing unit printson the preceding sheet and the preceding sheet is conveyed by the firstroller, and to drive the first roller not in synchronization withdriving of the second roller so as to make the succeeding sheet catch upwith the preceding sheet in a state where the printing unit prints onthe preceding sheet after the trailing edge of the preceding sheetpasses the first roller.
 27. The method according to claim 26, furthercomprising controlling to drive the first roller not in synchronizationwith driving of the second roller so as to make the succeeding sheetoverlap with the preceding sheet.
 28. The method according to claim 27,further comprising controlling the second roller to convey thesucceeding sheet to a position facing the printing unit in a state inwhich the succeeding sheet overlaps with the preceding sheet.